1. Field of the Invention
The present invention relates to an improved ultrasound probe and method of making an ultrasound probe for use in connection with a multi-lumen transport catheter. The present invention more particularly relates to an improved ultrasound probe that allows for more accurate ultrasound readings and has a relatively small outer diameter, such that it can be used in connection with an improved catheter which can accept various probes for sensing biological conditions and parameters and which allows high fluid flow rate for introducing fluids irrespective of the presence of sensing instruments in the catheter, thereby reducing the risk of patient complications.
2. Description of Related Art
Numerous catheters exist for sensing, diagnosing and treating various biologic conditions. For example, there are cardiac catheters used for angioplasty, for measuring cardiac output, such as thermodilution catheters, pulmonary artery wedge pressure monitors, blood flow monitors and temperature monitors. In use, a transport catheter is initially introduced into an appropriate vessel or body cavity. In the case of a thermodilution catheter, for example, the transport catheter may be introduced into an appropriate vein. Thereafter, the thermodilution catheter is inserted and passed through the right atrium and ventricle and out to the pulmonary artery. After the catheter is properly positioned and the balloon inflated, various readings can be taken of left heart pressure, for example, and pulmonary artery temperature. The same measurements may be taken a number of times while the catheter is in place. However, if the patient's condition changes and requires other measurements or diagnosis, or additional information is desired, such as may be required in view of the results obtained by the thermodilution measurements, the thermodilution catheter must be removed and substituted with a different catheter for such measurements. The subsequent catheter exchange increases the possibility of infection through the introduction of a second catheter and increases the probability of other problems such as venous puncture.
Another problem with frequent catheter exchange is that only physicians are authorized to remove and replace catheters and probes in the patient's body. However, after a physician has inserted and positioned the catheter in the patient's body, a trained nurse is permitted to insert, position, and replace probes within the catheter, since the probe does exit the catheter. Therefore, it is desirable to use a transport catheter in connection with a probe, such that the probe can be used within the transport catheter without the removal and replacement of the transport catheter.
In the past, multi-lumen catheters were designed wherein the catheter body was divided into circular sections of similar size or substantially triangular sections to form the separate lumens. These catheters were generally too small to accept sensing probes and one or more of the lumens of such catheters occasionally become constricted at the seal of the transport catheter. A further disadvantage of these multi-lumen catheters becomes apparent if an ultrasound probe was to be used within one of the lumens of the catheter in order to obtain diagnostic readings. In this case, the similar sized lumens surrounding the probe-carrying lumen contain relatively large amounts of air space that cause undesirable attenuation of the ultrasonic signal.
Undesirable signal attenuation is also caused by the transducer design of the prior art ultrasound probes. For example, ultrasound probe transducers may be formed of crystal material, having two leads attached to the crystal material. The first lead is connected to the inner surface of the crystal material, and the second lead is connected to the outer surface of the crystal material. The location of the second lead on the crystal material causes a "dead" spot in the attenuation pattern of the ultrasound signal. Therefore, the ultrasound probe does not provide as accurate of a reading as desired. Also, the attachment of the second lead to the outer surface of the crystal cylinder causes the outer diameter of the ultrasound probe to increase, making it difficult to fit the ultrasound probe within the transport catheter. Therefore, a need exists for an ultrasound probe having a relatively small outer diameter, and which does not produce dead spots in the attenuation pattern of the ultrasound signal.
In patients undergoing major surgery or suffering from serious illness, there is an acute need for a continuous blood flow measurement, as compared to an intermittent blood flow measurement. Therefore, ultrasonic transducer probes have been designed to continuously measure cardiac blood flow.
A known method of calculating blood flow is to multiply the area of the blood flow times the velocity of the flow. Methods have been developed for using ultrasound transducers to calculate the area and to calculate the blood flow velocity. For example, it is known to use echo patterns to determine the cross-sectional area of a blood vessel, and to use a Doppler technique to determine blood flow velocity.
However, in order to measure both cross-sectional area and velocity, two separate and distinct ultrasound transducer elements were used. A first transducer element was used to obtain measurements of the flow area, and a second transducer element was used to obtain measurements of the flow velocity. For example, in one method, several transducer elements are located at the catheter tip. A first plurality of transducer elements are activated and used to calculate the cross-sectional area of the vessel perpendicular to the catheter tip by echo methods. With the same catheter, a second distinct annular transducer element is activated to determine the velocity of the blood which flows perpendicular to the cross-sectional area. The velocity is determined by using the Doppler principle, wherein the Doppler shift created by the movement of the blood cells is analyzed. The product of the two measurements provides the blood flow measurement.
Another method of determining blood flow includes a method wherein the transducer generates a single large uniform cone-shaped beam which extends forwardly into the pulmonary artery. However, in this method, only a single cone-shaped beam is analyzed, and a radially-oriented beam is not utilized to determined the cross-sectional area of the artery.
With many of the known ultrasound probes, the probe must be axially aligned within the blood vessel and blood flow in order to provide an accurate reading. If the probe is not properly aligned, the angle of incidence between the probe axis and the blood flow adversely affects the accuracy of the ultrasound probe measurements. Therefore, a need exists for an ultrasound probe with a single transducer element that can generate a radially oriented signal beam and a forwardly oriented beam simultaneously, and which is not affected by the angle between the axis of the transducer and the blood flow.
There is also a need for an improved catheter which can accept an ultrasound probe, and which also, simultaneously, allows for high fluid flow for fluids to be introduced into the body, as well as the introduction of relatively viscous fluids. Additionally, a need exists for a multi-lumen catheter that minimizes the sizes of the lumens which might contain ultrasonic wave attenuating air in lumens adjacent an instrument containing lumen.